ThatMicPre - an open-source mic preamp

[antoine_glls]

Ah for some reason I hadn't thought of that. I found a 24V supply at a local electronics store and the preamp is working very well. Thank you for the design!

 

[zraxix]

Hi, and thanks for the great open design! I just put together my first ThatMicPre. However, the output is low and distorted even at the max gain. I've included some pics! Would appreciate it if anyone notices anything obviously out of place or can suggest troubleshooting advise! I'm running it into a Scarlett interface on using the line in port on the back, and powering off a bench top power supply.

 

[zraxix]

I would like to amend my previous statement. The distortion was due to a bad cable. The output however still seems very low

 

[georgenikolaou]

Hello guys,

thank you for this great project.
Please, I have a problem with the Matlab file.
I'm trying to use it but it gives me error.
Please could you inform me how to use it? What values and where I must put to give me results?

The version of Matlab that I'm using is R2023a

Thank you in advance.

 

[ojg]

Hi, and thanks for the great open design! I just put together my first ThatMicPre. However, the output is low and distorted even at the max gain. I've included some pics! Would appreciate it if anyone notices anything obviously out of place or can suggest troubleshooting advise! I'm running it into a Scarlett interface on using the line in port on the back, and powering off a bench top power supply.

Hi zraxix,

My first question is, what DC voltage are you suing ac power supply? 48V or at least 24V, I hope?

If that is correct then I would take out a multi-meter and measure the DC voltages at the V48P, V35P and V18P nodes.

 

[ojg]

Hello guys,

thank you for this great project.
Please, I have a problem with the Matlab file.
I'm trying to use it but it gives me error.
Please could you inform me how to use it? What values and where I must put to give me results?

The version of Matlab that I'm using is R2023a

Thank you in advance.

Hi georgenikolaou

Hard to help you without any more info. What is the exact error that you are getting?

How much prior experience do you have with Matlab or Octave? The file is a normal matlab function, the help text for the parameters show if you type "help micpre_gain2res"

 

[georgenikolaou]

Hello ojg,

Thank you for your reply.
Please attached you will find the error that it shows to me.
To be honest, I don't have an experience with Matlab.
Can you imagine which is the problem and what to change to have the results?

Thank you very much in advance.

 

[ojg]

You have misunderstood how you pass parameters to a Matlab function. You need to learn the basics of using Matlab first. There are many good Youtube videos on the subject.

 

[georgenikolaou]

Thank you Ojg, I will search it.

 

[georgenikolaou]

Hello,
Please, what's the input inpedance of your design? 2.4kΩ? I would like to use it with a dynamic Mic which has 320 ohm output impedance.
Is it suitable?

 

[ojg]

From the Github readme:

• Input impedance: 2.0kohm differential (1kHz)

 

[georgenikolaou]

Thank you Ojg.
Please which resistors change the input impedance?

 

[Niht]

Excellent project, I read the entire forum and I am encouraged to build it.
I have a question and sorry for the ignorance on the technical issue, why not power the preamplifier from the same 48v source of the console or audio card?

 

[unicast]

@Niht , I don't know the standard, but from my experience phantom gives ~10mA and this circuit requires ~30mA

 

[Mark Tillotson]

Phantom power is 48V through 6k8 ohms, or 7mA max per wire, so 14mA max total (with no voltage left!), or 7mA at 24V, or 5mA at 30V, etc etc.

 

[alauth]

Hi everyone !

I'm trying to build this project but I can't find any PDF of the panels so that I can drill the Hammond enclosure, does anyone have a way to generate them or should I download/install KiCAD to make them myself ? I'm building the rack version

Or maybe it's a bad idea to drill the front and back panels myself ?

Thanks everyone !

Cheers

 

[alauth]

Another question

I received all the parts but was surprised to see that I had 35V capacitor for C14 and C16. So I double checked the BOM and the code for C14 and C16 is UEP1V220MED which links to Nichicon 22 uF 35V DC.

Should I be worried to put these Nichicon 35V instead of the 50V as written on the schematic ? I'm afraid they would blow because of the 48V...

Should the BOM be updated ?

Thanks everyone !

 

[ojg]

Hi alauth!

Yes, that's a typo in the BOM, sorry. However 35V caps will be fine here because they will not get 48V across them, only 16V.

As for pdf for panels, there are some gerber to pdf tools out there, but I think it would be easier to just print it from KiCad directly. Drilling the panels yourself will work fine, I'm looking forward to seeing the results.

Br
OJG

 

[ojg]

Excellent project, I read the entire forum and I am encouraged to build it.
I have a question and sorry for the ignorance on the technical issue, why not power the preamplifier from the same 48v source of the console or audio card?

Hi,
If you have a console with 48V phantom then it probably has microphone preamp built in and you don't really need a preamp like this one.

 

[alauth]

Hi alauth!

Yes, that's a typo in the BOM, sorry. However 35V caps will be fine here because they will not get 48V across them, only 16V.

As for pdf for panels, there are some gerber to pdf tools out there, but I think it would be easier to just print it from KiCad directly. Drilling the panels yourself will work fine, I'm looking forward to seeing the results.

Br
OJG

Wow, that's some fast answer, thank you !

I'm currently downloading KiCAD, time for me to discover a new software

I'll probably build a 4 channel rack version in the future if this build works, I'll post pictures.

Thank you for this amazing project, I'm slowly transitioning from ready-to-go kit DIY projects to full DIY project and this one looks perfect. Next step will be designing it...!